In the field of refining of molten metal in a top-blowing oxygen converter, a control system based on the dynamic control has been developed for the purpose of saving labor in refining operations and automating the processes. A sub-lance for obtaining information and data concerning conditions of refining in the converter such as the chemical composition and the temperature of molten metal during refining is indispensable for said control system.
FIG. 1 is a schematic sectional view illustrating an embodiment of the aforementioned sub-lance. As shown in FIG. 1, a molten metal 5 is refined by inserting downward a main lance for blowing oxygen 2 substantially vertically into a top-blowing oxygen converter 1 containing a molten metal 5 to be refined, and by blowing pressurized oxygen onto the surface of said molten metal 5 through said main lance 2 at a certain position above the surface of said molten metal 5. On the other hand, sampling and temperature-measuring of said molten metal 5 are carried out by inserting downward a sub-lance 3 into said converter 1 substantially vertically at a proper timing, and by immersing a probe 7 for sampling and temperature-measuring of said molten metal 5, which is releasably fitted to the lowermost end of said sub-lance 3, into said molten metal 5.
In general, the sub-lance 3 is releasably fitted to a sub-lance carriage 10 as shown in FIG. 3. The sub-lance carriage 10 is suspended by a wire rope 11 and moves vertically together with the sub-lance 3 along a guide rail 9 provided on a turning frame 8 by hoisting up or down said wire rope 11 with the use of a winch (not shown). Sampling and temperature-measuring of said molten metal 5 in the converter 1 are therefore conducted by lowering the sub-lance 3 together with the sub-lance carriage 10 by hoisting down the wire rope 11 with the use of the winch, and by immersing the probe 7 fitted to the lowermost end of the sub-lance 3 into the molten metal 5. The sub-lance 3 is movable, as required, together with the sub-lance carriage 10, from outside to above the converter 3 and from above the converter 3 to outside, by turning the turning frame 8.
The sub-lance 3 usually has a concentric three-pipe structure comprising from inside to outside an air supply pipe, a water discharge pipe and a water supply pipe, and is cooled by cooling water during sampling and/or temperature-measuring the molten metal 5. To prevent slag from coming into the probe 7 when the probe 7 passes through the slag layer covering the surface of the molten metal 5, pressurized gas such as air and nitrogen is blown into the probe 7 through the air supply pipe.
However, the sub-lance 3 inserted into the converter 1 during refining of the molten metal 5 deflects inevitably toward the main lance 2 under the effect of the high temperature heat of the hot spot 6 where occur reactions between oxygen 4 blown from the main lance 2 and the molten metal 5 and the high temperature heat of molten metal and molten slag splashing and adhering onto the sub-lance 3. More specifically, as shown in the graph of FIG. 2, the sub-lance 3 deflects toward the main lance 2, under the effect of the above-mentioned heat affection, substantially in proportion to the number of repetitions of sampling and/or temperature-measuring during refining of the molten metal. Because of this deflection, it has been unavoidable that the following problems occurred in a conventional sub-lance 3 after being used several times:
(1) It becomes difficult to immerse straight vertically the probe 7 fitted to the lowermost end of the sub-lance 3 into the molten metal 5, and this causes troubles in sampling and/or temperature-measuring;
(2) The sub-lance 3 and the probe 7 become too close to the hot spot 6, or even come in the hot spot 6, thus causing burnout of the sub-lance 3 and the probe 7;
(3) The device (not shown) for engaging and disengaging the probe 7 with the lowermost end of the sub-lance 3 becomes unserviceable; and
(4) It becomes impossible for the sub-lance 3 to pass through a through-hole provided in a hood (not shown) which hangs over and covers the converter 1, and when the aforementioned deflection of the sub-lance 3 is serious, it may become necessary to remove the sub-lance 3 by flame cutting.
To avoid these inconveniences, prevention of the above-mentioned deflection of the sub-lance toward the main lance has been attempted through such measures as the enhancement of cooling of the sub-lance and the prevention of molten metal and molten slag from adhering onto the sub-lance. It was however impossible to ensure prevention of the aforementioned deflection of the sub-lance through these measures.
With a view to solving the above-mentioned problems involved in the conventional sub-lance, Japanese Patent Provisional Application No. 129,604/77, laid open on Oct. 31, 1977, discloses a method for sampling and temperature-measuring with a sub-lance, which comprises, after a certain number of repetitions of sampling and/or temperature-measuring, rotating the sub-lance around its axial line by about 180.degree., i.e., up to the direction just opposite to the direction of deflection of the sub-lance, and conducting sampling and/or temperature-measuring in the latter position several times, thus correcting the deflection toward the main lance (said method is hereinafter referred to as the "prior art").
According to said prior art, as shown in FIGS. 3 and 4, a sub-lance 3 is fitted to a sub-lance carriage 10, rotatably around the axial line of said sub-lance 3 and releasably from the sub-lance carriage 10. The sub-lance carriage 10, which is suspended by a wire rope, is vertically movable together with the sub-lance 3 along a guide rail 9 provided on a turning frame 8, through guide rollers 9a, by hoisting up or down the wire rope 11 through a winch (not shown).
The sub-lance 3 has a concentric three-pipe structure comprising from inside to outside an air supply pipe, a water discharge pipe and a water supply pipe. A water supply outer cylinder 12 having a water supply branch pipe 39 rotatably engages with the upper end portion of said water supply pipe through a bearing mechanism and a sealing mechanism. A water discharge outer cylinder 13 having a water discharge branch pipe 40 rotatably engages with the upper end portion of said water discharge pipe through a bearing mechanism and a sealing mechanism. When conducting sampling and/or temperature-measuring, the sub-lance 3 is cooled by cooling water which is supplied through the water supply branch pipe 39, the water supply outer cylinder 12 and the water supply pipe, and is discharged through the water discharge pipe, the water discharge outer cylinder 13 and the water discharge branch pipe 40. A probe 7 for sampling and temperature-measuring of molten metal is connected to the lowermost end of the air supply pipe, and a swivel joint 32 having an air supply branch pipe 32a rotatably engages with the upper end portion thereof. The air supply pipe, the water discharge pipe and the water supply pipe constituting the sub-lance 3 are fixed to each other by an appropriate means through a sealing mechanism. Therefore, when rotating the sub-lance 3 around the axial line thereof in a manner as described later, the air supply pipe, the water discharge pipe and the water supply pipe rotate as an integral body, and the water supply outer cylinder 12, the water discharge outer cylinder 13 and the swivel joint 32 never rotate together with the sub-lance 3. Even while rotating the sub-lance 3, therefore, it is possible to supply and discharge water and to supply air always at a prescribed position.
In FIG. 4, 17 is a drive mechanism including a reduction gear for rotating the sub-lance 3 around the axial line thereof. A chain 36 engages with a small sprocket 34 fitted to the axis of rotation of the drive mechanism 17 and with a large sprocket 35 fitted to the sub-lance 3, and permits rotation of the sub-lance 3 around the axial line thereof up to a desired angle by driving the drive mechanism 17. It is therefore possible to correct a deflection of the sub-lance 3, after using the sub-lance 3 several times for sampling and/or temperature-measuring during refining a molten metal in the converter, by ascertaining the direction and the degree of deflection of the sub-lance 3, then rotating the sub-lance 3 up to a direction opposite to the direction of deflection, i.e., by about 180.degree., and conducting sampling and/or temperature-measuring several times at the latter position. It is known that the drive mechanism 17, which is fitted to the sub-lance carriage 10 in FIG. 4, may be fitted to the water supply outer cylinder 12 or the water discharge outer cylinder 13. It is also known that the drive mechanism 17 may be actuated by remote operation.
In FIG. 4, 37 is a suspension fitting fixed to the upper end portion of the water discharge outer cylinder 13. The sub-lance 3 can be engaged with or disengaged from the sub-lance carriage 10 by hoisting up or down the suspension fitting 37 by a crane (not shown). More specifically, it is possible to easily engage the sub-lance 3 with the sub-lance carriage 10 by hoisting down the sub-lance 3 with the use of the crane and inserting the sub-lance 3 through a hole provided in a receiving stand (not shown) fixed to the upper end portion of the sub-lance carriage 10 and through a hole provided in a supporting device (not shown) fixed to the lower end portion of the sub-lance carriage 10. Sub-lance 3 can easily be disengaged from the sub-lance carriage 10 by hoisting up, with the use of the crane, the sub-lance 3 engaged with the sub-lance carriage 10 as mentioned above.
According to the prior art described above, it is possible to correct a deflection of the sub-lance toward the main lance occurring during refining of molten metal in a coverter. While it had been necessary to replace about 12 sub-lances per 1,000 times of sampling and/or temperature-measuring, said prior art eliminated the necessity of replacing the sub-lance after the same number of repetitions of sampling and/or temperature-measuring, and permitted sampling and/or temperature-measuring in a satisfactory condition, thus giving remarkable effects.
However, said prior art has the following drawbacks:
(1) As mentioned above, the water supply outer cylinder 12 and the water discharge outer cylinder 13 respectively engage rotatably with the water supply pipe and the water discharge pipe through a bearing mechanism and a sealing mechanism. Furthermore, the air supply pipe, the water discharge pipe and the water supply pipe constituting the sub-lance 3 are fixed to each other by an appropriate means through a sealing mechanism. However, when rotating the sub-lance 3 by the drive mechanism 17, a strong non-uniform force is applied to these sealing mechanisms, causing troubles in these sealing mechanisms, and thus may cause leakage of cooling water, a serious accident;
(2) When rotating the sub-lance 3 around the axial line thereof by the drive mechanism 17, it is not always easy to accurately detect the angle of rotation of the sub-lance 3. For this reason, it is difficult to rotate the sub-lance 3 by an appropriate angle of rotation for correcting the above-mentioned deflection of the sub-lance 3;
(3) Along with the recent trend of top-blowing oxygen converters becoming larger in size, the length of the sub-lance 3 also tends to increase even to over 20 meters in some cases. Even such a long sub-lance is fitted at the upper end portion thereof to a sub-lance carriage only at two points. It is therefore difficult not only to prevent swinging of the sub-lance during operation but also to align the sub-lance for holding it accurately in the vertical position.
Because of these drawbacks, said prior art was problematic, in spite of the excellent advantages as mentioned above, in that these advantages could not be fully utilized.